Fishing cormorants in China refused to work after their seventh fish
On the Li River, fishermen let their cormorants eat every eighth catch. Once a bird had delivered seven, it simply stopped, ignoring commands and even shoves until its neck ring was loosened. The observer concluded they could count to seven. Bird brains, it turns out, pack neurons far more densely than ours.
Measuring intelligence in animals is notoriously hard, but birds give researchers plenty to work with. Their brains are large relative to their heads and hold two to four times as many neurons per unit of volume as mammal brains. Sight and hearing are generally excellent, while touch and smell are well developed only in some groups, so tests usually rely on responses to visual and sound cues. Corvids, the crow family, and parrots stand out; both live socially, take a long time to mature and have large forebrains, traits thought to support sharper thinking.
Counting has long served as a yardstick. Anecdotes from the 1960s suggested crows count to three, and parrots have been shown to reach six, though scientists must rule out subitising, the instant recognition of very small quantities. The cormorant account came from Pamela Egremont, who watched Li River fishermen in the 1970s. Many birds also notice when eggs go missing from a nest, which is why parasitic cuckoos often remove a host egg before laying their own.
Learning experiments reveal intriguing trade-offs. Bebus and colleagues trained Florida scrub-jays to link coloured rings with food, then swapped the colours. Birds that learned the first rule quickly were slower to adjust when it flipped. Low levels of the stress hormone corticosterone predicted faster initial learning, and high levels better adjustment. Diet matters too, though findings conflict: one study linked high-protein diets in zebra finches to better learning, while another found underfed chicks did better on spatial tasks but had poorer memory.
Ecology and circumstance shape these abilities. Clayton and Krebs compared food-hoarding jays and marsh tits with non-hoarding jackdaws and blue tits on a hidden-food task. Among Australian magpies, adults solved a learning task more often, while juveniles were quicker to try it. And in pheasants released into the wild, fast learning helped heavy birds survive their first four months but seemed to hurt lighter ones.
Source: Bird intelligence
